Books and other bound paper items are a substantial part of many businesses, homes and institutions of learning. These printed materials are generally formed of multiple sheets or layers of paper. Although each sheet may not have a great individual thickness, the cumulative total of these pages requires significant linear shelf space.
Many facilities for retaining these publications have a fixed storage volume. Thus, many materials are either sent off site or destroyed. The destruction of materials presents numerous negative implications. However, even off site storage requires cataloging transport and maintenance of the materials, thereby adding to the overall cost. While publishers of books and other bound paper items recognize the shelf space problem, the publishers are limited to the thickness of paper they can employ. Most printing devices require the paper to have a minimum thickness, resistance to curl and other parameters that permit rapid processing of the paper. Therefore, the paper must have a certain thickness to print and the resulting publication has a corresponding thickness. This results in increased shelf space requirements of the publications. In addition, binding costs go up as the thickness of material to be bound increases.
One solution to this problem is to use thinner paper. However, thinner paper often is either unusable or frequently jams in many copiers and other image printing or transfer equipment. In the 1970s, the Xerox Corporation introduced a paper known as “micro-spheres” that incorporated miniature paper or plastic spheres for the purpose of reducing the overall weight of the paper and thereby a reduction in mailing costs over conventional paper by virtue of its lighter weight. This paper had the normal thickness of copier paper and worked well in copiers and printers without jamming. This paper is no longer used or manufactured today, but the technology exists for making it.
Therefore, there is an ongoing need for a method of manufacturing, using and processing an imaging substrate, wherein the substrate has a reduced thickness after it has been printed and processed.
Heretofore, a number of patents and publications have disclosed the manufacture of such substrates, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 3,293,114 issued Dec. 20, 1966 discloses papers useful in packaging, printing, preparation of containers and the like wherein hollow expanded spherical particles are incorporated into the paper pulp by admixture with the wet pulp prior to deposition on the screen. These papers demonstrate increase stiffness and increase caliper.
U.S. Pat. No. 3,556,934 represents a method of making papers similar to that described in U.S. Pat. No. 3,293,114, mentioned above, with the exception that this patent teaches the incorporation of the microspheres in an unexpanded state to the aqueous suspension and during the drying of the paper subjecting it to temperatures sufficient to cause the particles to expand within the paper sheet.
U.S. Pat. No. 3,779,951 issued Dec. 18, 1973 relates to an improved method for the expansion of expandable microspheres in the presence of water.
U.S. Pat. No. 3,941,634 issued Mar. 2, 1976 discloses a method for the preparation of paper containing plastic particles by forming two-spaced apart dewatered webs of cellulose fibers introducing expandable thermoplastic beads between the dewatered webs pressing the spaced apart partially dewatered webs together and subjecting this product to heat to at least partially dry the fibers and at least expand a portion of the beads.
U.S. Pat. No. 4,133,688 issued Jan. 9, 1979 discloses a photographic paper coated with a polyolefin on both sides wherein in the preparation of the paper, either non-inflated microspheres which are subsequently inflated during the drying of the paper or inflated microspheres are added to the pulp during preparation of the paper.
U.S. Pat. No. 4,268,615 issued May 19, 1981 relates to a method of producing a relief by forming a layer of a pattern on the surface of a sheet made of a material having the property of increasing in volume when heated, the pattern being made of the material having a stronger ability to absorb light than the aforesaid material, and then radiating a strong light uniformly on the entire surface of the sheet to selectively heat the portion of the sheet adjacent the undersurface of the pattern layer whereby the pattern layer is raised from the sheet surface. The sheet is prepared by mixing microcapsules and a binder such as vinyl acetate polymers.
In accordance with the present invention, there is provided a method for reducing a thickness of a compressible substrate bearing an image, the substrate having an initial thickness, comprising: applying a compressive force to the substrate to compress the substrate to a thickness less than the initial thickness, the compressive force selected to preclude the substrate returning to the initial thickness after removal of the compressive force therefrom; and concurrently applying heat to the substrate.
In accordance with another aspect of the present invention, there is provided a method for reducing a thickness of a substrate bearing an image, comprising: forming an image on a substrate, the substrate transformable from an imaging state having a first thickness to a compressed state having a second thickness thinner than the first thickness; and concurrently compressing and heating the imaged substrate to transform the substrate to the compressed state without substantially distorting the image.
In accordance with yet another aspect of the present invention, there is provided an apparatus for producing a compressed substrate having an image thereon, comprising: an imaging station for rendering an image onto the substrate when said substrate is in an uncompressed state; and a compressing station, operatively associated with the imaging station, to receive an uncompressed substrate with an image thereon and to apply a sufficient compressive force to the imaged substrate to reduce a thickness of the substrate and thereby produce a compressed substrate with an image thereon.
In accordance with a further aspect of the present invention, there is provided a method for reducing a thickness of a compressible substrate bearing an image, the substrate having an initial thickness, including: preparing a substrate comprising paper making fibers and a low density bulking material so as to produce a substrate having a first density; applying a compressive force to the substrate to compress the substrate to a thickness less than the initial thickness, thereby increasing the density of the substrate to a second density greater than the first density, the compressive force selected to preclude the substrate from returning to the initial thickness after removal of the compressive force; and applying heat to the substrate while applying the compressive force.
One aspect of the invention is based on the discovery that imaged substrate material may be calendered or compressed so as to reduce the thickness of the substrate and thereby increase the density of the substrate. This discovery enables the use of cut-sheet substrates in the formation of books and other bound documents, particularly substrates that are to be employed as pages within a book. This discovery avoids problems that arise in the storage and shipping of bound documents and other materials traditionally shipped to end-users. As a result of the present invention, it is entirely possible to provide a substrate sheet that is of sufficient thickness to feed and be imaged using conventional printing systems, such as xerographic printing systems, and as a result of post-printing compression, produce thinner printed sheets. The advantage of such post-processing is that the weight of the sheets may be reduced along with the thickness, so that shipping costs are reduced.
This aspect is further based on the discovery of techniques that can produce printed pages of varying density, as a function of the compression force applied to the pages during the calendering process. Hence, it is possible, as a result of the present invention, to produce pages that, while using the same substrate stock for input, are able to produce output pages of differing thicknesses/densities. An aspect of the invention can be implemented, for example, by a compression roller system for which the pressure of the compression nip therein may be adjusted.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.